The underlying gene is thought to be histone deacetylase 9 (HDAC9 ).4 Mice with a deficiency of the HDAC9 gene (HDAC9−/− apolipoprotein E–deficient) exhibit reduced aortic atherosclerosis compared with HDAC9+/+ apolipoprotein E–deficient mice that do not have a deficiency.6 Furthermore, HDAC9 expression is upregulated in symptomatic carotid atherosclerotic plaques in man.4 The gene discussed is APOE; the disease is aortic atherosclerosis.